Oxidizing fuel in multiple operating modes

ABSTRACT

A fuel oxidizer system is operated in a first operating mode. In the first operating mode, a mixture that includes fuel from a fuel source is compressed in a compressor of the fuel oxidizer system; the fuel of the compressed mixture is oxidized in a reaction chamber of the fuel oxidizer system; and the oxidized fuel is expanded to generate rotational kinetic energy. The fuel oxidizer system is operated in a second operating mode. In the second operating mode, fuel from the fuel source is directed to bypass the compressor, and the fuel that bypassed the compressor is oxidized in the reaction chamber.

BACKGROUND

This disclosure relates to oxidizing fuel. Methane or other waste fuel gas produced by landfills or other sources may be used to fuel a gas turbine system. In a conventional gas turbine system, fuel is combusted as it is injected into pressurized air, thereby heating and increasing the energy of the gas. The energy is then extracted from the heated gas with a turbine which converts the energy into kinetic energy. The kinetic energy may be used to drive another device, for example, a generator. In some cases, the gas turbine system is temporarily shut down (e.g., for repairs, maintenance, or other reasons), and the source continues to produce methane and/or other gases that may be harmful if leaked into the Earth's atmosphere.

SUMMARY

A fuel oxidizer system is operated in at least two operating modes. In a first operating mode, fuel is compressed in a compressor of the fuel oxidizer system, and the compressed fuel is oxidized in a reaction chamber of the fuel oxidizer system. In at least one additional operating mode, fuel is directed to bypass the compressor, and the fuel that bypassed the compressor is oxidized in the reaction chamber.

In one general aspect, a fuel oxidizer system is operated in a first operating mode. In the first operating mode, a mixture that includes fuel from a fuel source is compressed in a compressor of the fuel oxidizer system; the fuel of the compressed mixture is oxidized in a reaction chamber of the fuel oxidizer system; and the oxidized fuel is expanded to generate rotational kinetic energy. The fuel oxidizer system is operated in a second operating mode. In the second operating mode, fuel from the fuel source is directed to bypass the compressor, and the fuel that bypassed the compressor is oxidized in the reaction chamber.

In one general aspect, a fuel oxidizer system includes a compressor that has an air and fuel mixture inlet and a compressed mixture outlet. The compressor compresses an air and fuel mixture between the air and fuel mixture inlet and the compressed mixture outlet. The fuel oxidizer system includes a reaction chamber that receives the compressed mixture from the compressed mixture outlet. The reaction chamber oxidizes at least a portion of the fuel of the compressed mixture. The fuel oxidizer system includes a valve system that receives fuel from a fuel source and directs the fuel received from the fuel source to the reaction chamber either by directing the fuel to the air and fuel mixture inlet of the compressor or by directing the fuel to bypass the compressor.

Implementations can include one or more of the following features. Operating the fuel oxidizer system in the first operating mode includes outputting electrical energy based on the rotational kinetic energy. Operating the fuel oxidizer system in the second operating mode includes operating the fuel oxidizer system as a flare. Operating the fuel oxidizer system in the second operating mode includes operating the fuel oxidizer system as a thermal oxidizer. The fuel oxidizer system includes a turbine that receives the oxidized fuel from the reaction chamber and converts heat energy from the oxidized mixture into rotational movement. The turbine includes a turbine inlet, the turbine receives the oxidized mixture from the reaction chamber through the turbine inlet, and the reaction chamber is adapted to maintain a maximum temperature of the mixture in the reaction chamber substantially at or below a temperature of the turbine inlet. Expanding the oxidized fuel to generate rotational kinetic energy includes expanding the oxidized fuel in a turbine to rotate the turbine. Oxidizing the fuel of the compressed mixture includes controlling a maximum temperature of the fuel in the reaction chamber to be substantially at or below an inlet temperature of the turbine. Operating the fuel oxidizer system in the second operating mode includes preheating air and mixing the preheated air with the fuel that bypassed the compressor. Oxidizing the fuel of the compressed mixture includes initiating an oxidation reaction by gradually raising the temperature of the fuel above an auto-ignition temperature of the fuel. Oxidizing the fuel of the compressed mixture includes initiating an oxidation reaction substantially independent of an oxidation catalyst or an ignition source. The reaction chamber receives and oxidizes the fuel directed by the valve system to bypass the compressor. The fuel oxidizer system includes a blower that communicates air into the reaction chamber. The fuel oxidizer system includes an igniter that initiates combustion of fuel that bypasses the compressor. The reaction chamber is adapted to initiate oxidation of fuel that bypasses the compressor substantially independent of an igniter and substantially independent of an oxidation catalyst. The reaction chamber is adapted to initiate oxidation the fuel of the compressed mixture substantially independent of an igniter and substantially independent of an oxidation catalyst. The valve system includes a valve inlet in fluid communication with the fuel source, a first valve outlet in fluid communication with the air and fuel mixture inlet of the compressor, and a second valve outlet in fluid communication with the reaction chamber and adapted to direct fuel to bypass the compressor. The valve system includes multiple valves.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example fuel oxidizer system.

FIG. 2A illustrates the example fuel oxidizer system of FIG. 1 operating in a turbine mode.

FIG. 2B illustrates the example fuel oxidizer system of FIG. 1 operating in a flare mode.

FIG. 2C illustrates the example fuel oxidizer system of FIG. 1 operating in a thermal oxidizer mode.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a diagram of an example fuel oxidizer system 100 that includes a reaction chamber 10 that oxidizes fuel. The system 100 may be operated in different modes of operation. When operated in a gas turbine mode, the system 100 compresses an air/fuel mixture in a compressor 6, directs the compressed air/fuel mixture to the reaction chamber 10, and drives a turbine 7 using the oxidation product from the reaction chamber 10. When operated in a flare mode or in a thermal oxidizer mode, the system 100 directs fuel into the reaction chamber 10 along a fuel flow path that bypasses the compressor 6. In the flare mode, the reaction chamber 10 oxidizes the fuel in a flame combustion process. In the thermal oxidizer mode, the reaction chamber 10 oxidizes the fuel in a flameless oxidation process. FIG. 2A illustrates the system 100 operating in gas turbine mode, FIG. 2B illustrates the system 100 operating in flare mode, and FIG. 2C illustrates the system 100 operating in thermal oxidizer mode. The system 100 can efficiently utilize waste gases (e.g., to generate kinetic and/or electrical energy), destroy waste gases and/or harmful components of waste gases (e.g., VOCs), and/or reduce unwanted emissions (e.g., NOx) that may be associated with combustion of waste gases. For example, the system 100 can reduce methane gas emission from landfills and/or significantly reduce emission of nitrogen oxides caused by flaring waste gases in some conventional systems.

The example system 100 oxidizes fuel received from a landfill. The landfill emits landfill gases that include methane gas, organic materials, and/or other components that are potentially harmful to the Earth's atmosphere. Regulations (e.g., government agency regulations, landfill regulations, private regulations, and others) may require that certain types of landfill gas components (e.g., methane, VOCs, and/or others) be reduced or eliminated before the landfill gas is discharged into the Earth's atmosphere. In the gas turbine mode, the system 100 can oxidize potentially harmful landfill gas components in connection with outputting electrical energy. When the system 100 is unavailable for generating electrical energy, the system 100 can operate in the flare mode or the thermal oxidizer mode to destroy the potentially harmful landfill gas components without requiring a separate combustion system or oxidation chamber. The system 100 can use a single reaction chamber to function as a power generation system, a flare system, or a thermal oxidizer system. Thus, the system 100 can reduce costs and/or hardware requirements associated with destroying potentially harmful landfill gases. Further, in some cases, the system 100 can reduce emissions below what is accomplished by a conventional flare.

The system 100 includes a fuel inlet 1 that receives fuel from a fuel source 20. In the illustrated example, the fuel source 20 is a landfill, and the fuel includes methane gas generated by decomposition of organic materials in the landfill. A blower 2 in fluid communication with the inlet 1 can generate directional fuel flow from the inlet 1 to a fuel distribution valve system including a first valve 4, a second valve 15, and/or a third valve 30. In some implementations, the fuel distribution valve system includes a different number of valves, such as one, two, four, or more valves. The fuel distribution valve system is changeable to distribute the fuel flow to either a gas mixer 5 through valve 4, the reaction chamber 10 through valve 15, a blower 16 through valve 30, or any combination of these. The valve 4 controls fuel flow from the blower 2 to the gas mixer 5. The valve 15 controls fuel flow from the blower 2 to the reaction chamber 10. The valve 30 controls fuel flow from the blower 2 to the blower 16.

The gas mixer 5 can mix fuel received from the fuel source 20 with air received from an air source (e.g., collected from a surrounding atmosphere). The gas mixer 5 can generate an air/fuel mixture having an air to fuel ratio in a specified range. The compressor 6 is in fluid communication with the gas mixer 5 and can compress an air/fuel mixture received from the gas mixer 5. The compressor 6 is mechanically coupled to the turbine 7 by a shaft 25. The shaft 25 may also couple to an auxiliary system, such as a generator 17. The generator 17 can convert rotational motion of the shaft 25 to electrical energy. A recuperator 8 is in fluid communication with the compressor 6, the gas turbine 7, the reaction chamber 10, and an exhaust path 12 a. The recuperator 8 is a heat exchanger that can receive exhaust gas from the gas turbine 7 and transfer heat energy from the received exhaust gas to the compressed air/fuel mixture received from the compressor 6. Thus, the recuperator 8 can impart heat energy to the compressed air/fuel mixture. A check valve 9 controls the direction of flow between the recuperator 8 and the reaction chamber 10. The valve 9 allows the heated and compressed air/fuel mixture to flow from the recuperator 8 into the reaction chamber 10 and prevents or reduces fluid flow into the recuperator 8 from the reaction chamber 10.

The blower 16 provides a separate flow to the reaction chamber 10. The blower 16 can receive air from an air source (e.g., an atmosphere of the blower 16, or another source) and generate a directional flow into the reaction chamber 10. The blower 16 can also receive fuel from the fuel source 20 and provide a flow of a mixture of air and fuel to the reaction chamber 10. In some cases, the flow from the blower 16 is heated by the heat exchanger 19. In some cases, the flow from the blower 16 bypasses the heat exchanger 19. For example, valves 26 and 27 can direct the flow to the heat exchanger 19 or to bypass the heat exchanger 19. The heat exchanger 19 is in fluid communication with the blower 16 through valve 26, the reaction chamber 10 through valve 22 and valve 21, and an exhaust path 12 b. The heat exchanger 19 can receive exhaust gas from the reaction chamber 10 through valve 21 and transfer heat energy from the received exhaust gas to air received from the blower 16. Thus, the heat exchanger 19 can impart heat energy to the air flow between the blower 16 and the reaction chamber 10.

The reaction chamber 10 includes an igniter 18, an aspirator 23, multiple inlets and multiple outlets. The igniter 18 can be a spark plug or another ignition source that produces a spark or a flame to ignite fuel. In the illustrated example, the aspirator 23 receives heated air from the heat exchanger 19 and disperses the heated air into the reaction chamber 10. In some implementations, the system 100 is configured differently, and the aspirator 23 receives fuel from the blower 2 and disperses the fuel into the reaction chamber 10. In some implementations, the reaction chamber can include a cylindrical liner that defines a flow path within the reaction chamber 10. In some implementations, the flow path within the reaction chamber 10 is defined by additional and/or different features of the reaction chamber 10. The reaction chamber 10 may include insulating refractory material, heat-absorbing material, heat-insulating material, and/or other materials. For example, the liner may include rock, ceramic, and/or or other materials that have a high thermal mass. In some implementations, a catalyst material is provided in the reaction chamber 10. Catalyst materials can promote initiation and/or completion of an oxidation reaction. Example catalyst materials include platinum and others. In some cases, no catalyst material is provided in the reaction chamber 10. In some implementations, the reaction chamber 10 can operate as the example reaction chamber described in U.S. patent application Ser. No. 12/050,734 entitled “Oxidizing Fuel.”

Each inlet and outlet of the reaction chamber 10 is connected to a valve that controls flow through the inlet or outlet. For example, valves 9, 14, 15, 21, 22 and 30, as well as other valves in the system 100 can allow flow, prevent flow, or control a rate of flow into and/or out of the reaction chamber 10. Valve 9 controls fuel flow from the compressor 6 into the reaction chamber 10. Valve 15 controls fuel flow from the diverter into the reaction chamber 10. Valve 22 (along with valves 26 and/or 27) controls air flow from the blower 16 into the reaction chamber 10. Valve 14 controls an exhaust flow exiting the reaction chamber 10 to the turbine 7. Valve 24 controls the exhaust flow from the reaction chamber 10 to the exhaust path 12 c. Valve 21 controls the exhaust flow from the reaction chamber 10 to the heat exchanger 19. FIGS. 2A, 2B, and 2C illustrate the valves in various configurations for different modes of operation of the system 100.

FIG. 2A illustrates the example fuel oxidizer system 100 operating in a gas turbine mode, where the system 100 oxidizes fuel received from the fuel source 20 to output electrical energy. In the gas turbine mode shown, valve 4 and valve 14 are open, and valve 15, valve 21, valve 22, valve 24, valve 26, valve 27 and valve 30 are closed. Arrows in FIG. 2A illustrate flow in the gas turbine mode of operation. The fuel inlet 1 receives fuel from the fuel source 20. The blower 2 directs fuel received from the fuel inlet 1 to the gas mixer 5 through valve 4. The gas mixer 5 mixes the fuel with air collected from an atmosphere or a different source to produce an air/fuel mixture. The compressor 6 receives the air/fuel mixture from the gas mixer 5 and compresses the received mixture. The recuperator 8 receives die compressed air/fuel mixture from the compressor 6 and heats the received mixture. The reaction chamber 10 receives the heated and compressed air/fuel mixture from the recuperator 8 through the check valve 9.

The fuel is oxidized as the air/fuel mixture flows along the flow path defined in the reaction chamber 10. The fuel may be oxidized by a flameless gradual oxidation process that destroys substantially all of the fuel. The fuel may be oxidized at a temperature sufficiently low to reduce or prevent formation and/or emission of harmful compounds, such as nitrogen oxides. The air/fuel mixture flows through the reaction chamber 10. The air fuel mixture may absorb heat from the interior surface of the reaction chamber 10, and as a result, the temperature of the air/fuel mixture may gradually increase as the mixture flows through the reaction chamber 10. When the temperature of the air/fuel mixture reaches or exceeds an auto-ignition temperature of the fuel, the fuel undergoes an exothermic oxidation reaction. Thus, the oxidation reaction may be initiated independent of an oxidation catalyst material or an ignition source. In some cases, a catalyst material may be provided in the reaction chamber 10 to effectively lower the auto-ignition temperature of the fuel. When the fuel oxidizes, the exothermic reaction may impart heat to the reaction chamber 10, and the reaction chamber 10 may communicate the heat energy to another region of the flow path in the reaction chamber 10. The heat energy transferred through the reaction chamber 10 may be imparted to incoming fuel to help initiate oxidation of the incoming fuel. The reaction chamber 10 may be designed such that under a range of operating conditions (e.g. at maximum flow rate and fuel concentration), sufficient dwell time and fuel temperature are provided to allow some or all of the fuels in the air/fuel mixture to oxidize substantially to completion. In some cases, the temperature of the air/fuel mixture in the reaction chamber 10 can be controlled to maintain the maximum temperature of the air/fuel mixture substantially at or below a desired inlet temperature of the turbine 7. The desired inlet temperature of the turbine 7 may be a temperature recommended by a manufacturer of the turbine 7, a temperature that accomplishes an intended or desired output of the turbine 7, or another temperature.

Exhaust gas that includes the oxidation product exits the reaction chamber 10 and flows into the turbine 7 through valve 14. The exhaust gas expands in the turbine 7, producing rotational movement of the shaft 25 and the compressor 6. The rotation of the shaft 25 also drives the generator 17. The generator 17 generates electrical energy based on kinetic energy imparted to the generator 17 from the turbine 7 (e.g., kinetic energy communicated from the turbine 7 by rotation of the shaft 25). The generator 17 may output electrical energy to an electrical system, a power storage device, a power grid, or another type of system. The turbine 7 communicates the expanded exhaust gas into the recuperator 8. The recuperator 8 transfers heat energy from the exhaust gas to the air/fuel mixture received from the compressor 6. From the recuperator 8, the exhaust gas exits the system 100 through the exhaust flow path 12 a.

FIG. 2B illustrates the example fuel oxidizer system of FIG. 1 operating in a flare mode, wherein the system 100 destroys fuel and/or other components of gas received from the fuel source 20. The system 100 may be operated in the flare mode apart from outputting electricity. The system 100 may be operated in the flare mode when one or more components of the system 100 is unavailable for operation. For example, the flare mode may be used to destroy landfill gas components when maintenance, repair, and/or other types of activities are being performed on the compressor 6, the turbine 7, the generator 17, the recupertor 8, and/or other components of the system 100. The flare mode uses the reaction chamber 10 to eliminate VOCs and/or other components of fluids received from the fuel source 20. Thus, the flare mode does not require a separate reaction chamber for operation. In the flare mode shown, valve 4, valve 14, valve 21, valve 22, valve 26, valve 27 and valve 30 are closed, and valve 15, and valve 24 are open.

Arrows in FIG. 2B illustrate flow in the flare mode of operation. The fuel inlet 1 receives fuel from the fuel source 20. The blower 2 directs fuel received from the fuel inlet 1 to the reaction chamber 10 through valve 15. The blower 16 may generate air flow into the reaction chamber 10 through valve 22, and/or an induced air flow 31 may be received into the reaction chamber 10. When the blower 16 induces air flow into the reaction chamber, the air flow may be heated by the heat exchanger 19 or the air flow may bypass the heat exchanger. The induced air flow 31 may be received into the reaction through the aspirator 23 or through another type of inlet or device.

Arrows in the reaction chamber 10 illustrate an example flow path of the fuel through the reaction chamber 10 in flare mode. The induced air flow 31 is introduced in the reaction chamber 10. In some implementations of the flare mode, the fuel and/or the air flow is introduced in the reaction chamber through the aspirator 23. The air and fuel mix to form an air/fuel mixture in the reaction chamber 10, or in some cases, prior to entering the reaction chamber 10. The igniter 18 initiates a flame combustion reaction of the air and fuel by igniting the air/fuel mixture. Methane gas, VOCs, and/or other landfill gas components may be destroyed as a result of the flame combustion reaction. The air/fuel mixture flows generally in an axial direction through the interior of the reaction chamber 10. Exhaust from the flame combustion reaction exits the reaction chamber 10 through valve 24. In the illustrated flare mode of operation, exhaust from the reaction chamber 10 may exit the system 100 through the exhaust path 12 c.

FIG. 2C illustrates the example fuel oxidizer system of FIG. 1 operating in a thermal oxidizer mode, where the system 100 destroys fuel and/or other components of gas received from the fuel source 20. The system 100 may be operated in the thermal oxidizer mode apart from outputting electricity. The system 100 may be operated in the thermal oxidizer mode when one or more components of the system 100 is unavailable for operation. For example, the thermal oxidizer mode may be used when maintenance, repair, and/or other types of activities are being performed on the compressor 6, the turbine 7, the generator 17, the recupertor 8, and/or other components of the system 100. The thermal oxidizer mode uses the reaction chamber 10 to eliminate VOCs and/or other components while reducing the emission of byproducts (e.g., NOx, and/or others) associated with some combustion reactions. Thus, the thermal oxidizer mode does not require a separate reaction chamber for operation. In the thermal oxidizer mode shown, valve 4, valve 14, valve 15, valve 24, and valve 27 are closed, and valve 21, valve 22, valve 26, and valve 30 are open.

Arrows in FIG. 2C illustrate flow in the thermal oxidizer mode of operation. The fuel inlet 1 receives fuel from the fuel source 20. The blower 2 directs fuel received from the fuel inlet 1 to the blower 16 through valve 30. The blower 16 generates a flow of air/fuel mixture into the reaction chamber 10 through valve 22. In the thermal oxidizer mode shown, the air flow from the blower 16 flows through valve 26 and receives heat energy while passing through the heat exchanger 19. In some implementations of the thermal oxidizer mode, some or all of the air flow from the blower 16 bypasses the heat exchanger 19 through valve 27.

Arrows in the reaction chamber 10 in FIG. 2C illustrate an example flow path of the fuel through the reaction chamber 10 in the thermal oxidizer mode. In some implementations of the thermal oxidizer mode, air flow, fuel flow, and/or a flow of air/fuel mixture can be introduced in the reaction chamber 10 through the aspirator 23. The air and fuel can mix in the reaction chamber 10 to form an air/fuel mixture, or in some implementations, the air and fuel are mixed prior to entering the reaction chamber 10, for example, in the blower 16. The fuel may be oxidized by a flameless gradual oxidation process that destroys substantially all of the fuel. The fuel may be oxidized at a temperature sufficiently low to reduce or prevent formation and/or emission of harmful compounds, such as nitrogen oxides. When the temperature of the air/fuel mixture reaches or exceeds an auto-ignition temperature of the fuel, the fuel undergoes an exothermic oxidation reaction. Thus, the oxidation reaction may be initiated independent of an oxidation catalyst material or an ignition source. In some cases, a catalyst material may be provided in the reaction chamber 10 to effectively lower the auto-ignition temperature of the fuel. The air/fuel mixture flows generally in an axial direction through the interior of the reaction chamber 10. Exhaust from the flameless oxidation reaction exits the reaction chamber 10 through valve 21. In the illustrated thermal oxidizer mode of operation, exhaust from the reaction chamber 10 may impart heat energy to the heat exchanger 19 and exit the system 100 through the exhaust path 12 b.

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims. 

What is claimed is:
 1. A fuel oxidizer system comprising: a compressor that has a mixture inlet and a compressed mixture outlet and is configured to compress an air and fuel mixture between the mixture inlet and the compressed mixture outlet; a reaction chamber configured to receive a compressed mixture from the compressed mixture outlet and oxidize at least a portion of the fuel of the compressed mixture to produce an oxidation product; a turbine; a first valve system, comprising a first valve disposed along a first flow path and a second valve disposed along a second flow path, configured to receive fuel from a fuel source and direct the fuel to the reaction chamber (i) by directing the fuel to the mixture inlet of the compressor via the first valve, in a first mode, and (ii) by directing the fuel to bypass the compressor via the second valve, in a second mode; and a second valve system configured to receive the oxidation product from the reaction chamber and direct the oxidation product (i) to the turbine via a third flow path, in the first mode, and (ii) to an exhaust path, bypassing the turbine via a fourth flow path, in the second mode.
 2. The fuel oxidizer system of claim 1, wherein the reaction chamber is configured to receive and oxidize the fuel directed by the first valve system to bypass the compressor.
 3. The fuel oxidizer system of claim 1, wherein the turbine is configured to receive the oxidized fuel from the reaction chamber and convert heat energy from the oxidized mixture into rotational movement.
 4. The fuel oxidizer system of claim 1, wherein the turbine comprises a turbine inlet, the turbine being configured to receive the oxidized mixture from the reaction chamber through the turbine inlet, and the reaction chamber is configured to maintain a maximum temperature of the mixture in the reaction chamber substantially at or below a temperature of the turbine inlet.
 5. The fuel oxidizer system of claim 1, further comprising a blower between the fuel source and the reaction chamber.
 6. The fuel oxidizer system of claim 1, the reaction chamber comprising an igniter that is configured to initiate combustion of fuel to bypass the compressor.
 7. The fuel oxidizer system of claim 1, wherein the reaction chamber is configured to initiate oxidation of fuel to bypass the compressor substantially independent of an igniter and substantially independent of an oxidation catalyst.
 8. The fuel oxidizer system of claim 1, wherein the reaction chamber is configured to initiate oxidation the fuel of the compressed mixture substantially independent of an igniter and substantially independent of an oxidation catalyst.
 9. The fuel oxidizer system of claim 1, wherein the first valve system comprises an inlet of the first valve in fluid communication with the fuel source, an outlet of the first valve in fluid communication with the mixture inlet of the compressor, an inlet of the second valve in fluid communication with the fuel source, and an outlet of the second valve in fluid communication with the reaction chamber and configured to direct fuel to bypass the compressor.
 10. The fuel oxidizer system of claim 1, wherein the first valve system comprises multiple valves.
 11. The fuel oxidizer system of claim 1, further comprising a heat exchanger between the fuel source and the reaction chamber.
 12. The fuel oxidizer system of claim 11, wherein, in the second mode, the first valve system is configured to direct the fuel through the heat exchanger.
 13. The fuel oxidizer system of claim 11, wherein, in the second mode, the second valve system is configured to direct the oxidation product through the heat exchanger.
 14. The fuel oxidizer system of claim 5, wherein, in the second mode, the blower is configured to receive the fuel from the fuel source and air from an air source to provide a flow of a mixture of air and fuel to the reaction chamber. 